The present invention relates to a facsimile apparatus having recording means of the type causing a light emitting device to emit light in response to data received from an external channel so as to form a corresponding image on a photoconductive element, and then recording the image on a recording medium.
It is a common practice with a facsimile apparatus to represent record pixel density by a metric system, e.g., 8.times.3.85 pixels per millimeter or 8.times.7.7 pixels per millimeter, as prescribed by the CCITT agreement. On the other hand, regarding recording devices, the pixel density is often represented in inches, e.g., 240 dots per inch (dpi).times.240 dpi. This brings about a problem that the difference in standard prevents received facsimile data from being transferred to and recorded by a recording device in various manners. To eliminate this problem, the received data may be thinned or interpolated to match the standards. However, the standards cannot be matched unless the difference in pixel density is 2.sup.n times. In light of this, Japanese Patent Laid-Open Publication (Kokai) No. 82010/1989 discloses an apparatus which produces clear-cut images by changing the rotation speed of a polygon motor and the frequency of a pixel synchronization signal and, therefore, the record pixel density. In this case, to prevent the overall image density from changing, the size of a record pixel may be changed by a variable restriction generally referred to as an aperture, as also proposed in the past. Further, there has been known a facsimile apparatus operable, in a facsimile mode, to transform multilevel image data generated by a scanner and representative of a document to bilevel image data, compress it, and then transmit it and, in a copy mode, to transfer the multilevel image data directly to a recording section.
Assume that a facsimile apparatus reads thin oblique lines at a density corresponding to the standard recording density of 8.times.3.85 pixels per millimeter and sends the resulting data to a remote facsimile apparatus. Then, when the receiving apparatus receives and records the data, it is likely that the oblique lines appear partly discontinuous since image data representative of a line thinner than the pixel is sometimes converted to a white pixel in the event of digitization. In light of this, it has been customary with the transmitting apparatus to slightly increase the values of image data read representative of a document or to execute image processing using a spatial filter. However, such a scheme is successful only with a popular apparatus having a relatively large recording dot size. Specifically, in a popular apparatus, when the low line density data mentioned above is received and recorded by a recording device, an acceptable image can be recorded with the defects of the transmitted image corrected. By contrast, when it comes to a recording device whose recording density is as high as 16 lines per millimeter, which is now attracting attention, the pixel size is small to render the entire image faint while discontinuous lines are exaggerated due to high definition.
Today, recycled papers and color papers are increasingly used to save limited natural resources and to enhance color sensation, respectively. When such papers are used to record images, the image density relative to the background density is lowered to render images illegible. Moreover, when these papers are thin and used to record an image on both sides thereof, the image on the rear is apt to interfere with the image on the front due to transmission.